1、SAE Technical Standards Board Rules provide that: “This report is published by SAE to advance the state of technical and enginee ring sciences. The use of this report is entirelyvoluntary, and its applicability and suitability for any particular use, including any patent infringement arising therefr
2、om, is the sole responsibility of the user.”SAE reviews each technical report at least every five years at which time it may be reaffirmed, revised, or cancelled. SAE invit es your written comments and suggestions.Copyright 1998 Society of Automotive Engineers, Inc.All rights reserved. Printed in U.
3、S.A.QUESTIONS REGARDING THIS DOCUMENT: (724) 772-8510 FAX: (724) 776-0243TO PLACE A DOCUMENT ORDER: (724) 776-4970 FAX: (724) 776-0790SAE WEB ADDRESS http:/www.sae.org400 Commonwealth Drive, Warrendale, PA 15096-0001AEROS PACE INFORM ATION REPORTSubmitted for recognition as an American National Stan
4、dardAIR947Issued 1971-02Reaffirmed 1998-02E ngine E rosion P rotectionFOREWORDChanges in this reaffirm are format/editorial only.1. SCOPE:This Aerospace Information Report deals with protection of helicopter aircraft engines against erosion. Applicability is restricted to aircraft having a disc load
5、ing of less than 15 pounds per square foot.2. BACKGROUND:Historically, the responsibility for providing the means of handling the problem of entrainment of undesired substances in the inlet air of aircraft gas turbines has been an interface problem between the engine and airframe manufacturer; howev
6、er, the trend has clearly been in accordance with two basic principles:(a) Whatever substances can possibly be tolerated in the air should be allowed to remain, and the engine designer is responsible to allow for them. Examples of such substances are snow, rain, hail, supercooled water droplets, and
7、 reasonable quantities of small, solid particules such as sand, dust, foliage, etc. Tolerance of the engine is optimized in design and development (i.e., an anti-icing system is provided, and erosion resistant materials are used in engine construction).(b) Whatever substance cannot be tolerated in t
8、he air must be removed by an airframe part or an engine accessory, if available. Examples of such substances are bolts, nuts, rags, hay, and large quantities of sand and dust.A more fundamental underlying principle from which the foregoing are derived is that the solution for any problem associated
9、with entrainment should be undertaken by whichever manufacturer can provide the best solution to the problem from an overall aspect.SAE AIR947- 2 -3. QUANTITY OF SAND AND DUST WHICH CAN BE TOLERATED IN ENGINE INLET AIR:Determination of the quantity of sand and dust which can be tolerated in any give
10、n engine is a complex problem. Generation of this answer poses a major difficulty inasmuch as the tolerance of an engine for sands of different chemical composition, different particle size, and size distribution has not yet been predicted analytically. Furthermore, the experimental determination of
11、 the effects of these variables is a very costly proposition. One practical approach is the use of a standard test sand which can be used to define the tolerance of a given engine. The various branches of the Government are attempting to develop such a standard and contract for a defined tolerance i
12、n the procurement of new engine models. Specifications must be established for materials to be used as design criteria for engines and inlet systems. There is considerable variation in tolerance of one engine design to another, and there are trade-offs in performance in selecting a design. Thus, it
13、is not desirable to impose an overly stringent tolerance on the engine (which is likely to be at the expense of performance) when a less stringent engine tolerance requirement could result in a better aircraft by the inclusion of a sand separator. On the other hand, a minimum engine tolerance is nec
14、essary.4. TEST CONCEPTS FOR EROSION TOLERANCE:In view of the fact that the concept of a representative “test sand” is strongly entrenched in Industry and Government thinking, it is expedient to further this concept to the point that sufficient understanding is achieved to result in an agreeable stan
15、dard.Choice of “ Test Sand”Military specifications for gas turbines have recognized two standard sands for a number of years. These are known as “Coarse Arizona Road Dust” and “Fine Arizona Road Dust”. They have been used for environmental testing, and have been found satisfactory for most purposes.
16、 However, it has been established that they are not representative of helicopter environments in many operating areas. The reason is two-fold: First, they consist of particles which are considerably smaller than those contained in sandy soil. Second, the chemical composition, being only 68% Silica,
17、is not as abrasive as pure quartz found in beach sand. Helicopters (depending on design and disc loading) have been shown to be capable of stirring up an entire soil spectrum of particle sizes, and the engines have ingested almost the entire spectrum, with very little selectivity for the finer parti
18、cles, as would normally be expected. Particles of 500 microns and above can be so ingested.Because of the shortcomings of “coarse” and “fine” Arizona Road Dust, as test sands for helicopters, there has been increasing effort to find a new standard consisting of larger particle size and more abrasive
19、 material. Several are under study. Figure 1 shows the particle size distribution of four samples of sandy soil from widely scattered areas of the world. Figure 2 represents two test sands. One of these, which contains some larger particle sizes, is defined in Military SpecificationMIL-E-5007C (Engi
20、nes, Aircraft, Turbojet and Turbofan, General Specification for, Paragraph 3.25). The material is crushed quartz, a more abrasive material than that found in “Coarse Arizona Road Dust.” This test material is more representative of sandy soils, and thus simulates the type of environment which would b
21、e experienced by a helicopter engine operating without any protection such as a barrier filter or sand separator. It would also represent the best simulation of the operating environment of a combined engine-separator package.SAE AIR947- 3 -4. (Continued):Small engines used in small aircraft do not
22、appear to be subjected to the large particle sizes which constitute the largest fraction of MIL-E-5007C contaminant. In order to simulate the environment for these engines, the use of Arizona Coarse Road Dust is recommended. The choice of test sand should hinge on the size and expected environment o
23、f the aircraft.As an objective, the following degree of tolerance is recommended:1. For engine-separator packages:(a) MIL-E-5007C test sand at a rate of ingestion of .006 grams per cubic foot of total aspirated air for a duration of 50 hours minimum, from uneroded engine condition, and(b) “Coarse Ar
24、izona Road Dust” at a rate of ingestion of .006 grams per cubic foot of total aspirated air for a duration of 50 hours minimum, from uneroded engine condition.2. For bare engines:(a) MIL-E-5007C test sand at a rate of ingestion of .0015 grams per cubic foot of air for a duration of 3 hours 20 minute
25、s minimum, from uneroded engine condition, or(b) “Coarse Arizona Road Dust” at a rate of ingestion of .0015 grams per cubic foot of air for a duration of 10 hours minimum, from uneroded engine condition.5. ESTABLISHING THE REQUIREMENTS FOR A SEPARATOR:Tolerance of a given engine against sand ingesti
26、on can best be presented in the form of performance change plotted against weight of sand ingested for each test sand. Rate of ingestion should be specified, as well as any limiting failure criteria, such as surge or part failure. Knowing the tolerance of a given engine, the aircraft designer can de
27、fine the requirements for a separator (or no separator, as the case may be). This determination must be made with the knowledge of the conditions under which the aircraft will operate, and how long it will be exposed to sand and dust during each mission. Unfortunately, data is not available on how m
28、uch sand will become suspended in the air and taken into the engine inlets. This depends on the downwash, flow pattern, and relative location of cowling and engine inlet. Until these influences are better understood, the selection of separator requirements will have to be partly based on experience
29、with similar type aircraft.SAE AIR947- 4 -6. DESIGN GUIDELINES FOR PARTICLE SEPARATORS:Whether the separator is airframe or engine mounted, the design goals are the same: high efficiency of collection combined with low pressure drop, low weight, and low cost. There are trade-offs in these objectives
30、 with each separator concept, which the designer may wish to explore for his particular application. However, certain criteria have achieved a measure of standardization, and these are listed as follows:a. Efficiency of Separation85% by weight of MIL-E-5007C test sand or Coarse Arizona Road Dust at
31、normal rated power. This is a mean figure; good efficiency is above 90%; poor efficiency is below 80%.b. Pressure Drop1% of total pressure.c. WeightMinimum design weight consistent with other requirements.d. Anti-IcingIf the separator is sensitive to icing to the degree that it would be a limitation
32、 on operation of the aircraft in icing conditions, then a bypass should be provided which can be opened to provide direct access of inlet air to the engine, or the critical icing surfaces of the separator should be protected.e. Ram RecoverySeparators should be designed to recover the ram pressure ri
33、se insofar as it is practical to do so. If necessary, a bypass system may be used to achieve this result.f. Disposal of Separated SandContinuous self-purging of the separated sand is highly desirable, provided the mechanical power and ejection hardware is not an excessive penalty. Disposal must be l
34、ocated at a point on the aircraft where the sand cannot be re-ingested into the engine.If the separator is not self-purging, then a sufficient volume must be provided to hold at least the quantity of sand which would accumulate during 10 hours of operation in an environment having a sand concentrati
35、on of 0.006 grams per cubic foot of air.SAE AIR947- 5 -6. (Continued):g. Effects of RainConsideration must be given to the problems which arise when water is introduced in combination (or alternately) with sand and dust. The most formidable of these is the formation of caked mud in various areas or
36、passages of the separator. Adequate provisions must be provided to facilitate cleaning, even though it may be impossible to maintain the full efficiency of separation during operation in such environments. If the possibility exists that build-up of caked mud could restrict airflow to the engine, the
37、n a bypass is mandatory.h. Structural RequirementsIf airframe mounted, the structural requirements must be equal to those contained in the detail specifications for a particular model aircraft.If engine mounted, the separator should comply with the qualification procedures required for the engine, a
38、nd be tested with the engine as an engine part, or engine accessory.i. TestingEnvironmental testing should be conducted to demonstrate compliance with the appropriate paragraphs of MIL-E-5272C. An additional test requirement, as determined from experience associated with operation in sandy environme
39、nt peculiar to separators must define functional and life requirements, applicable design guides and test procedures to establish conformance. Performance and life of components such as blowers, bearings, seals, and ducts are examples of items which will conform to these additional requirements.Efficiency of separation should be demonstrated by a full scale test which includes the effects of the location of the engine inlet geometry in the aircraft fuselage mock-up.PREPARED BY SAE COMMITTEE S-12, HELICOPTER POWERPLANTSAE AIR947- 6 -FIGURE 1SAE AIR947- 7 -FIGURE 2
